| Children with reading disability tend to name visually presented stimuli more slowly, and with more difficulty, than normally-achieving readers. While rapid naming is a well-established phenotypic correlate of reading performance, it has been less subject to genetic analysis than reading disability, and few studies have attempted to assess the causes of their covariation. The purpose of this dissertation was to perform the first full autosomal genome screen for rapid naming, and to test the hypothesis that previously localized QTL for reading disability may also have pleiotropic effects (i.e., multiple effects of a single gene) for slower performance on rapid naming tasks.; The participants included 503 individuals from 119 families (a total of 179 DZ twin and nontwin sibling pairs) who were tested through the Colorado Learning Disabilities Research Center and genotyped at the University of Oxford. Twin pairs in which at least one member demonstrated evidence of reading problems, and their siblings, completed an extensive battery of psychometric tests, including the numbers, colors, pictures, and letters subtests of the rapid naming paradigm, phonological decoding and orthographic coding tests, and the Peabody Individual Achievement Test. DZ twins pairs, any available siblings of MZ and DZ twins over 8 years of age who were willing to participate in the study, and both parents from each family were genotyped for 391 autosomal markers using blood or buccal samples. Univariate DeFries-Fulker (DF) linkage models for the analysis of selected sib-pair data were employed to perform singlepoint and multipoint genome screens of rapid naming. The bivariate adaptation of the DeFries-Fulker linkage model was then fit to the data to test for pleiotropic effects of QTL on both reading and rapid naming deficits.; Results from univariate singlepoint and multipoint genome screens of the rapid naming composites localized susceptibility loci for rapid naming deficits to some of the same chromosomal regions where QTL for reading difficulties have been previously reported. In addition, QTL affecting variance in rapid naming performance were localized to several novel chromosomal regions. Finally, results obtained from bivariate linkage analyses indicate that previously localized susceptibility genes for reading disability on chromosomes 3, 6, and 18 may also have pleiotropic effects on rapid naming tasks. |
